In general, an air conditioner for a vehicle includes a cooling system for cooling the interior of the vehicle and a heating system for heating the interior of the vehicle. At an evaporator side of a refrigerant cycle, the cooling system converts air into cold air by heat-exchanging the air passing outside an evaporator with refrigerant flowing inside the evaporator so as to cool the interior of the vehicle. At a heater core side of a cooling water cycle, the heating system converts air into warm air by heat-exchanging the air passing outside the heater core with cooling water flowing inside the heater core so as to heat the interior of the vehicle.
In the meantime, differently from the air conditioner for the vehicle, a heat pump system which can selectively carry out cooling and heating by converting a flow direction of refrigerant using one refrigerant cycle has been applied. For instance, the heat pump system includes two heat exchangers: one being an internal heat exchanger mounted inside an air-conditioning case for heat-exchanging with air blown to the interior of the vehicle; and the other one being an external heat exchanger for heat-exchanging outside the air-conditioning case, and a direction-adjustable valve for changing a flow direction of refrigerant. Therefore, according to the flow direction of the refrigerant by the direction-adjustable valve, the internal heat exchanger serves as a heat exchanger for cooling when the cooling mode is operated, and serves as a heat exchanger for heating when the heating mode is operated.
Various kinds of the heat pump system for the vehicle have been proposed, and FIG. 1 illustrates a representative example of the heat pump system for the vehicle.
As shown in FIG. 1, the heat pump system for the vehicle includes: a compressor 30 for compressing and discharging refrigerant; an internal heat exchanger 32 for radiating heat of the refrigerant discharged from the compressor 30; a first expansion valve 34 and a first bypass valve 36 mounted in parallel for selectively passing the refrigerant passing through the internal heat exchanger 32; an external heat exchanger 48 for heat-exchanging the refrigerant passing through the first expansion valve 34 or the first bypass valve 36 with the outdoor; an evaporator 60 for evaporating the refrigerant passing through the external heat exchanger 48; an accumulator 62 for dividing the refrigerant passing through the evaporator 60 into a gas-phase refrigerant and a liquid-phase refrigerant; an inside heat exchanger 50 for heat-exchanging refrigerant supplied to the evaporator 60 with refrigerant returning to the compressor 30; a second expansion valve 56 for selectively expanding the refrigerant supplied to the evaporator 60; and a second bypass valve 58 mounted in parallel with the second expansion valve 56 for selectively connecting an outlet side of the external heat exchanger 48 and an inlet side of the accumulator 62.
In FIG. 1, the reference numeral 10 designates an air-conditioning case in which the internal heat exchanger 32 and the evaporator 60 are encased, the reference numeral 12 designates a temperature-adjustable door for controlling a mixed amount of cold air and warm air, and the reference numeral 20 designates a blower mounted at an inlet of the air-conditioning case.
According to the heat pump system having the above structure, when a heat pump mode (maximum heating mode) is operated, the first bypass valve 36 and the second expansion valve 56 are closed, and the first expansion valve 34 and the second bypass valve 58 are opened. Moreover, the temperature-adjustable door 12 is operated as shown in FIG. 1. Accordingly, the refrigerant discharged from the compressor 30 passes through the internal heat exchanger 32, the first expansion valve 34, the external heat exchanger 48, a high pressure side 52 of the inside heat exchanger 50, the second bypass valve 58, the accumulator 62, and a low pressure side 54 of the inside heat exchanger 50 in order, and then, is returned to the compressor 30. That is, the internal heat exchanger 32 serves as a heater and the external heat exchanger 48 serves as an evaporator.
When an air-conditioning mode (maximum cooling mode) is operated, the first bypass valve 36 and the second expansion valve 56 are opened, and the first expansion valve 34 and the second bypass valve 58 are closed. Furthermore, the temperature-adjustable door 12 closes a passage of the internal heat exchanger 32. Therefore, the refrigerant discharged from the compressor 30 passes through the internal heat exchanger 32, the first bypass valve 36, the external heat exchanger 48, the high pressure side 52 of the inside heat exchanger 50, the second expansion valve 56, the evaporator 60, the accumulator 62, and the low pressure side 54 of the inside heat exchanger 50 in order, and then, is returned to the compressor 30. In this instance, the internal heat exchanger 32 closed by the temperature-adjustable door 12 serves as a heater in the same with the heat pump mode.
However, in case of the conventional heat pump system for the vehicle, in the heat pump mode, the internal heat exchanger 32 mounted inside the air-conditioning case 10 serves as a heater so as to carry out heating, and the external heat exchanger 48 mounted outside the air-conditioning case 10, namely, at the front side of an engine room of the vehicle, serves as an evaporator which exchanges heat with the outdoor air.
In this instance, if temperature of the external heat exchanger 48 becomes lower than freezing point while the refrigerant introduced into the external heat exchanger 48 exchanges heat, with the outdoor air, frosting is formed on the surface of the external heat exchanger 48.
When frosting on the surface of the external heat exchanger 48 is expanded continuously, the external heat exchanger 48 cannot absorb heat and it causes drop of temperature and pressure of the refrigerant inside the system and drop of temperature of the air discharged to the inside of the vehicle so as to remarkably reduce heating performance, such that it deteriorates stability of the system because liquid refrigerant is induced into the compressor
Therefore, the conventional heat pump system for the vehicle is controlled to stop operation when frosting is formed on the external heat exchanger 48 to start operation again when frosting is removed. As described above, because heating performance is deteriorated when the heat pump system stops operation when frosting is formed, an electric heater is operated. Then, consumption of electrical power increases, and it reduces the mileage of electric vehicles or hybrid vehicles.
Moreover, when it snows, snow is accumulated on the external heat exchanger 48, such that the external heat exchanger 48 is stopped. As described above, in the state where snow is accumulated on the external heat exchanger 48, when the vehicle enters into the idle state, excessive noise is generated due to operation of a fan of the external heat exchanger.